Field of the Disclosure
The present invention relates to an organic light emitting display device, and more particularly, to an organic light emitting display device which is capable of maintaining a uniform luminance between each of sub-pixels.
Discussion of the Related Art
An organic light emitting display device includes an organic light emitting layer which emits light by recombination of hole and electron, whereby the organic light emitting display device emits light in itself. Also, since the organic light emitting display device emits light in itself, there is no problem related with a viewing angle. In addition, the organic light emitting display device has advantages of rapid response speed and low power consumption. In this respect, the organic light emitting display device has been attracted as a next-generation flat panel display.
The organic light emitting display device may include a plurality of sub-pixels for displaying images. Each sub-pixel may include an organic light emitting diode having an organic light emitting layer between anode and cathode electrodes, and a pixel circuit for making the organic light emitting diode emit light. The pixel circuit may include a switching transistor, a driving transistor, and a capacitor. The switching transistor is switched by a gate signal, and the switching transistor supplies a data voltage to the driving transistor. The driving transistor is switched by a data voltage supplied from the switching transistor, and the driving transistor controls a current flowing to the organic light emitting diode, and also controls a light emission of the organic light emitting diode. The capacitor stores a voltage between gate and source terminals of the driving transistor, and switches the driving transistor by the use of stored voltage. The organic light emitting diode emits light by the current supplied from the driving transistor.
In the organic light emitting display device according to the related art, a characteristic variation of the driving transistor such as mobility and threshold voltage (Vth) of the driving transistor may occur in each sub-pixel due to a manufacturing deviation, whereby an amount of current for driving the organic light emitting diode may vary, and thus a luminance deviation may occur between each of sub-pixels. In order to overcome this problem, the Unexamined Korean Patent Publication Number P10-2013-0066449 having counterpart US 2013/0147694 A1 (hereinafter, referred to as related art document’) discloses an external compensation technique for compensating the characteristic variation of sub-pixel by sensing the characteristic variation of sub-pixel from the outside of the sub-pixel and reflecting the sensing result on data of the sub-pixel.
In the above-mentioned related art document, the organic light emitting diode emits light by a current based on a differential voltage between a data voltage supplied to a gate electrode of driving transistor included in each sub-pixel and a reference voltage supplied to a source electrode of driving transistor, to thereby display desired images.
However, in the case of the related art document, the reference voltage having a constant DC level is generated from an external voltage supply, and is then supplied to all sub-pixels in common. Thus, even though a threshold voltage of the driving transistor included in each sub-pixel is compensated by a data correction, the reference voltage supplied to each sub-pixel is not uniform so that a luminance deviation occurs between each of the sub-pixels, which results in deterioration of luminance uniformity in a low grayscale level.